Tablets metadata is quite expensive to generate (each data_value is
an allocation), so an old driver (without support for tablets) will
generate huge amounts of such notifications. This commit adds a way
to negotiate generation of the notification: a new driver will ask
for them, and an old driver won't get them. It uses the
OPTIONS/SUPPORTED/STARTUP protocol described in native_protocol_v4.spec.
Closesscylladb/scylladb#16611
Previously, the tablet information was sent to the drivers
in two pieces within the custom_payload. We had information
about the replicas under the `tablet_replicas` key and token range
information under `token_range`. These names were quite generic
and might have caused problems for other custom_payload users.
Additionally, dividing the information into two pieces raised
the question of what to do if one key is present while the other
is missing.
This commit changes the serialization mechanism to pack all information
under one specific name, `tablets-routing-v1`.
From: Sylwia Szunejko <sylwia.szunejko@scylladb.com>
Closesscylladb/scylladb#16148
